Method of making electroformed articles



Patented July 21, .1953

UNITED?- STATES PATENT:

OFFICE METHOD OF MAKING ELECTROFORMED ARTICLES Reginald s. Dean, Washington, 1). o.

- N0 Drawing. Application March 17, 1949,

Serial No. 81,999

This invention relates to electroforming and stripping. 'is minimized." .It also has for its object the provision of a cathode base for electroforming which can be used repeatedly without treatment. Stillanother object is the production of an electroformed article having a smooth, clean and uncontaminated surface. In the known art 'a wide variety of method havebeen used to obtain easily strippable oath-- ode deposits Without danger of premature peel ing. .Such methods include the coating of thecathode base metal with'graphite, grease, silicates and the like. They also include elaborate special means of preparing the cathode surface, such as. etching, sandblasting and buffing and combinations of these various surface preparation methods, in an attempt to achievethe desired compromise between strippability and premature peeling. Most of these methods must be repeated after each use of the cathode and none of them provide a surface suitable for repeated use without reworking.

I have found that these difiiculties can be avoided by carrying out'the electrodeposition so as to deposit the desired metal on a clean, passive surface of a metal selected from the group,

titanium and zirconium and alloys composed predominantly of metals of this group.

Themethod can be used forthe electroforming of a large number of metals. Infact all metals which can'be electrodeposited in coherent form from. aqueous'electrolytes can be electro formed into the desired articles and stripped from the starting cathodes by the application of this invention. This will'be illustrated by specific examples given hereinafter.

One advantage of the process is that neither the electrolyte nor'the electroformed material is contaminated since the cathode base'is unattacked by either acid or alkaline electrolytes even when current is not flowing. This renders unnecessary any protection ofthe cathode base at the solution line. The deposited material is 7 completely unalloyed since the diffusion of the terials and the formation of a passive surface 4 Claims. (c1.*2o4-,-12)

under all conditions of use. This advantage is particularly important when depositing a metal like manganese in which the form of the metal is affected by the cathode base: Copper, for example, tends to encourage the deposition of gamma manganese. In the method of the presentinvention there is no chemical or latticesimilarity influence of the cathode base on the, structure of the metal deposited. Thisstructure can, therefore, be controlled by other means.

The passivation of the metal surface is important. The metals of the described group are readily passivated and under most conditionsv of plating retain their passivity. Simple exposure to air'is adequate to supply the necessary passivity in most cases. The metal after fabrication is usually pickled with hydrofluoric acid and after this treatment it is thoroughly washed and exposed to air for a short period. Alternatively, it is momentarily made an anode in a dilute sulphuric acid solution. In this way a current blocking film is quickly formed which, however, is removed when the metal is made a cathode for plating, leaving only the passivity required for this invention. The passivity of these metals results intheir failure to show an electrochemical potential against other metals in the usual electrolytes. This is an advantage as no stray currents are set up between the cathode base and the metal electroplated on it. i

Having now described the general features of my invention I give the following illustrative examples.

Example I I take a sheet of. ductile titanium and prepare hydrofluoricacid. I then' polish the surface with the finest, emery and rouge. and then clean thoroughly in an. alkaline cleaner, followed by 2% sulphuric acid. .The clean surface is allowed to dry in air for '15 minutes to insure passivation. I then plate this surface with copper from a. slightly acid solution of copper sulphate to a thicknessof .0905 of an inch. This thin copper sheet is readily separated from the titanium and is smooth. bright and clean and readyfor many uses in the arts. The titanium cathode base is re-used WithOLlt further treatment for the preparation of several hundred such copper sheets.

' Example II I take a sheet of titanium and etch it deeply by immersing in 10%. hydrofluoric acid. This etched titanium sheet is passivated by exposure to air and is used as a cathode in the electrowinning of manganese in accordance with the generally known process of deposition from a solution of manganese and ammonium sulphate. In the known art stainless steel cathodes are used after elaborate preparation and are buffed and otherwise treated before each use to insure good stripping. The etched and passivated titanium cathodes are used in the ordinary Way in a manganese electrowinning cell. The deposited manganese is readily and completely stripped .by a simple flexing operation. The etching of the cathode prevents any premature peeling of the deposit.

In distinction from the usual stainless steel cathodes the titanium cathodes may be repeatedly used without any treatment. Should any manganese incidentally adhere to the edges or' otherwise, it can be removed by sulphuric acid without affecting the cathodeswhich after such treatment and drying in air are ready to use again.

Example III by a twisting motion. The resulting chromium tube is bright, clean and uncontaminated and the cathode rod of zirconium may be repeatedly reused. 7

Example IV I take titanium sponge as prepared by the distillation of the magnesium chloride from the reduct-ion mixture of titanium and magnesium chloride which is formed by reducing TiCl4 with magnesium. This sponge is pure and very soft. I press a compact of this sponge into a die so as to provide a surface with a depressed design. In a specific example, I press the titanium sponge onto a form set with type. I now use the compressed titanium compact as the cathode base for plating copper which readily fills in the depressed design and after plating is easily stripped from the titanium to give a printing plate with the type in a raised position.

Example V I Eor some purposes a cathode base for electroforming having a high strength and hardness is desirable. and manganese may be employed.

In a specific example I take an alloy of 5% manganese, about .'70% carbon and balance titanium and hot forge to about the desired size. I then grind and polish the surface, clean with 10% hydrofluoric acid, repolish and expose to air. The cathode base prepared in this way is hard so that'it retains its exact dimensions with many uses. The cathode base is plated with nickel from a nickel sulphate solution and the nickel stripped from the cathode.

Example VI In another example I make use of the known property of the metals, titanium, zirconium and their alloys, to mark on glass. For example, I rule a fine network on a glass plate with a piece of passivated ductile titanium. I then plate this For. this purpose alloys of titanium 4 titanium network with nickel. The nickel strips readily from the titanium so that I obtain a very thin, fine mesh screen.

Example VII In another example I take a glass cylinder and rule many fine titanium lines around it. I then arrange a suitable sliding contact to each line and slowlyrotate the cylinder partially immersed in a copper sulphate solution. I make the lines a cathode and place a suitably disposed anode in the solution. The very fine copper strip which is plated on each line is stripped and coiled continuously to provide very fine, thin copper strip which is suitable for twisted electrical conductors.

Example VIII I take a sheet of titanium and perforate it to form a screen or sieve. I clean and polish the plate in accordance with Example I. I then electroplate the perforated plate with nickel to a thickness of .001 of an inch. I strip the nickel from the titanium and use the deposited metal sheet as a screen or sieve. An unlimited number of such screens or sieves can be made fro the original cathode base.

The examples given are to be regarded as illustrative only. It should be understood, for example, that zirconium, titanium and alloys of zirconium and titanium are alternatively usable in the process. It has been pointed out that zirconium is somewhat more acid resistant and will accordingly be selected when a highly acid electrolyte is to be used in the process. Likewise, when great hardness or strength and toughness are required, an alloy will be selected. Such selection of the cathode material from among the materials herein disclosed involves only engineering skill and can be made by those skilled in the art from published information. With regard to alloys, these will contain at least of titanium and zirconium. A sufficient number of such alloys have been tested to establish that so far as suitability for the present invention is concerned all may be used. The selection of suitable alloys within this group is, therefore, a matter of their known mechanical properties. The following alloying components have been found useful in forming alloys of titanium and of zirconium for production of operable cathodes: oxygen, nitrogen, aluminum, manganese, boron, silicon, iron, molybdenum, and tantalum.

What is claimed is:

1. The cyclical process of electrolytically depositing a metal on a cathode surface selected from the group consisting of titanium and zirconium of at least 90% purity, which comprises initially preparing the cathode surface by cleaning and washing the same and passivating it by exposure to air, and thereafter at least once executing the sequence of steps consisting in depositing said metal from an aqueous solution of a salt thereof onto said cathode surface, removing the cathode and its attached deposit from the electrolyte, mechanically stripping the deposit from the cathode surface, exposing the cathode to air and replacing the cathode in said solution, and then at least once repeating said sequence of steps.

2. The cyclical process defined in claim 1, in which the cathode surface is titanium.

3. The cyclical process defined in claim 1, in which the cathode surface is titanium and the electrodeposited metal is manganese.

4. The cyclical process of electroforming manganese which comprises initially preparing the surface of a cathode, consisting of titanium of at least 90% purity, by cleaning and washing the same and passivating it by exposing to air, and thereafter at least once executing the sequence of steps consisting in electro-depositing manganese from an electrolyte consisting essentially of an aqueous solution of manganese and ammonium sulphate onto said cathode surface, removing the cathode and its attached deposit of manganese from the electrolyte, mechanically stripping the manganese deposit from the cathode surface, exposing the cathode to air and replacing the cathode in said electrolyte, and then at least once repeating said sequence of steps.

REGINALD S. DEAN.

References Cited in the file of this patent UNITED STATES PATENTS Number 6 Number Name Date 1,861,625 Driggs June 7, 1932 2,203,253 Brown June 4, 1940 2,227,454 Kushner Jan. 7, 1941 2,279,567 Holman Apr. 14, 1942 2,292,026 Gillett Aug. 4, 1942 2,325,660 Chamberlain Aug. 3, 1943 2,433,441 Davidofi Dec. 30-, 1947 2,529,086 Law Nov. 7, 1950 FOREIGN PATENTS Number Country Date 436,282 Great Britain Oct. 9, 1935 OTHER REFERENCES Plating, Jan. 1948, pages 39-42 and 45.

Transactions of the American Institute of Mining and Metallurgical Engineers, vol. 166, 1946, pages 379-381. 

1. THE CYCLICAL PROCESS OF ELECTROLYTICALLY DEPOSITING A METAL ON A CATHODE SURFACE SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM OF AT LEAST 90% PURITY, WHICH COMPRISES INITIALLY PREPARING THE CATHODE SURFACE BY CLEANING AND WASHING THE SAME AND PASSIVATING IT BY EXPOSURE TO AIR, AND THEREAFTER AT LEAST ONCE EXECUTING THE SEQUENCE OF STEPS CONSISTING IN DEPOSITING SAID METAL FROM AN AQUEOUS SOLUTION OF A SALT THEREOF ONTO SAID CATHODE SURFACE, REMOVING THE CATHODE AND ITS ATTACHED DEPOSIT FROM THE ELECTROLYTE, MECHANICALLY STRIPPING THE DEPOSIT FROM THE CATHODE SURFACE, EXPOSING THE CATHODE TO AIR AND REPLACING THE CATHODE IN SAID SOLUTION, AND THEN AT LEAST ONCE REPEATING SAID SEQUENCE OF STEPS. 